Control heat exchanger

ABSTRACT

A heat exchanger ( 10 ) has an outer housing ( 16 ) and a first helical fluid flow path or coil ( 12 ) located in the housing ( 16 ) defining a plurality of turns and having an inlet ( 24 ) and an outlet ( 22 ) for entry and exit of fluid into the flow path to be heated or cooled. A second helical coil ( 14 ) defining a second fluid flow path is located within the housing ( 16 ) adjacent to the first coil. The second coil also has an inlet ( 24 ) and outlet ( 22 ) for a passage for hot or cold service media. A conductive or non-conductive sheath ( 18 ) is disposed between the coils. A transfer medium is disposed in the housing for transfer of heat between the first and second flow paths. A plurality of baffles ( 20 ) are located between the outer housing and sheath and disposed between turns of the first coil. A plurality of baffles ( 21 ) are also disposed between turns of the second coil ( 14 ). By interposing a transfer medium between the two fluid flow paths rather than having one of the fluid flows as the medium itself, control over the cooling or heating of the fluid to be heated or cooled is possible. The fluid being cooled or heated and fluid transfer medium may be at different temperatures. The sheath ( 18 ) and baffles ( 20, 21 ) help control the transfer of heat and improve the efficiency of the heat exchanger.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Australian ProvisionalPatent 2005901721 filed on 7 Apr. 2005, the content of which isincorporated herein by reference.

1. Field of the Invention

This Invention relates to heat exchangers and, in particular, toimprovements in the control of heat exchangers, particularly to heatexchangers for liquid or gaseous heat exchange to fluids. In moreparticular aspects, the invention is concerned with heat exchangers forcooling liquids, particularly beverages such as beer or soft drinks,although the principals of the invention could equally be applied toheating, or cooling, other fluids.

2. Background of the Invention

Heat exchangers are commonly used in clubs, bars, hotels and othervenues to chill beverages, typically, from a temperature of around 20°to 30° C. to around 0° C. for sale to patrons. Such heat exchangers areusually installed under a traditional bench or bar top.

Existing technology for cooling beverages, such as beer, prior todispensing from a tap, tends to be relatively large and consequently,rather expensive. Many of the larger cooling installations are set up tochill numerous lines of beer prior to dispensing it from one of a numberof taps, but also typically chill a number of glass cabinets forpre-chilling the glasses into which beverages are dispensed.

There is a need for a low cost compact system for dispensing beveragesfor smaller venues such as restaurants which may sell only one or twodifferent beverages and will only require one or more chilling anddispensing lines. The existing installations which are used in pubs,clubs and hotels are all too large and expensive.

One further problem with dispensing beverages, such as beer from a tap,is that the beverage companies such as brewers and soft drinkmanufacturers, often require their beverages to be dispensed at aparticular temperature or within a particular range of temperatures. Forexample beers, are typically required to be sold at a temperature ofbetween 2 and 4° C. inside the glass which means that the beer has bedispensed from the tap in a hotel at around 0.5 to 1° C. to allow forthe heat capacity of the glass which will typically be at a temperatureof greater than 4° C. The dispensing temperature of 0.5 to 1° C. isapproaching the freezing temperature for beer and if a beer tap islittle used and the beer over chilled, there is a risk that the beerwill freeze in the pipes of the dispensing apparatus. At the same time,the dispensing apparatus must be sufficiently efficient to be able todispense beer at the correct temperature as prescribed by the beveragecompany and on demand.

The present invention aims to address or alleviate at least some of theproblems of the prior art discussed above.

The present invention also aims to apply any solutions to the problemsdiscussed above to other fields where heat exchangers are or may beutilised.

Any discussion of documents, act, materials, devices, articles or thelike which has been included in the present specification is solely forthe purpose of providing a context for the present invention. It is notbe taken as an admission that any or all of these matters form part ofthe prior art base or were common general knowledge in the fieldrelevant to the present invention as it existed before the priority dateof each claim of this application.

SUMMARY OF THE INVENTION

In a first broad aspect, the present invention provides a heat exchangerincluding:

an outer housing;

a first means defining a first fluid flow path located in the housing,the first fluid flow path defining a plurality of turns and having aninlet and an outlet for entry and exit of fluid into the flow path to beheated or cooled:

a second means defining a second fluid flow path located within thehousing adjacent to the first flow path, said second fluid flow pathdefining a plurality of turns and having inlet and outlet for a passagefor hot or cold service media;

a sheath disposed between the first and second means;

a transfer medium disposed in the housing for transfer of heat betweenthe first and second flow paths, using either a static or a flowingtransfer medium;

preferably, a plurality of conductive baffles located between the outerhousing and sheath and disposed between turns of the first fluid flowpath; and

preferably, a plurality of conductive baffles disposed between turns ofthe second fluid flow path.

In one preferred embodiment, the sheath may have a relatively high heatconductivity and be made of e.g. metal. The baffles may also be made ofthe same or a different material having a relatively high heatconductivity, such as metal.

In an alternative embodiment, the sheath and/or baffles may be made of aless conductive material such as a plastics material.

The sheath may be conductive and the baffles non-conductive.

By interposing a transfer medium between the two fluid flow paths ratherthan having one of the fluid flows as the medium itself, control overthe cooling or heating of the fluid to be heated or cooled is possible.The fluid being cooled or heated and fluid transfer medium may be atdifferent temperatures. The sheath and baffles help control the transferof heat and improve the efficiency of the heat exchanger.

The heat transfer medium may be fluid, static or in motion, or a solid,depending on the application. Where the heat transfer medium is a fluid,any liquid or even a gaseous medium may be used but is most preferably aliquid medium. For the beverage dispensing application discussed above,a mixture of water and antifreeze, is particularly suitable but otherfluids may be used to suit the application and the desiredperformance/inefficiency characteristics required.

Typically, the first and second fluid flow paths comprise helical coilswith the second (inner) helical coil being of a relatively narrowerdiameter than the first (outer) helical coil and nested around thesheath which is located between the coils. The helical coils mosttypically have a circular cross section defining an interior and anexterior.

Where conductive baffles are inserted into the helix of each fluid flowpath coil between turns of the helix, these confer thermal energy to thecoils as well as defining a generally serpentine fluid flow path for thetransfer media when the transfer media is in motion.

This results in heat transfer arising from both conduction andconvection and considerably increases the efficiency of the system.

The housing is typically cylindrical having an annular cross-section andmost typically comprises a metal or other material with a highcoefficient of heat transfer. The beverage carried by the first coil istypically beer, although it may be a non alcoholic beverage or otherliquid product. Typically, the second coil carries a gaseousrefrigerant, typically a fluorocarbon such as R22 etc. or may be aliquid media such as hot water.

The second coil is in juxtaposition to the first coil and the sheath tooptimise conductive heat transfer, between the outer coil and the innercoil. The baffles optimise convective heat transfer between the innerand outer coils where the heat transfer media is in motion.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments of the invention will now be described by way ofexample only and with reference to the accompanying drawing in which:

FIG. 1 is a perspective view of a heat exchanger embodying the presentinvention; and

FIG. 2 is a schematic arrangement of a heat exchanger with a heattransfer media in motion.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Turning to the drawings, FIG. 1 shows a heat exchanger 10 comprisingfirst (outer) and second (inner) helical coils 12 and 14 respectivelylocated inside a housing 16 in the form of a hollow cylindrical housinghaving an annular cross section. a sheath 18 sits between coils 12 and14. In the described embodiment the sheath is conductive being made ofmetal, typically stainless steel however, it is envisaged that for someapplications, the sheath need not be conductive. Baffles 20 which is thedescribed embodiment are conductive, but which may not be in someapplications, are located between the turns of the coil 12 and extendbetween the conductive sheath 18 and the housing 16. Each baffle is inthe form of an annulus with the interior diameter of the annulusapproximately equal to the external diameter of the sheath and the outerdiameter approximately equal to the internal diameter of the housing. Aradial slit extends across each annulus. When inserted between coils ofthe outer coil, with the slits offset by 180°, the baffles have theeffect of making fluid travelling between the housing and the conductivesheath travel in a generally helical serpentine path, generallyfollowing the spiral of the helical coil 12, but reversing directionevery 180° and effectively travelling the full length of the coil.

A series of conductive baffles 21 are also disposed between coils of theinner coil 14 inside the conductive sheath 18. These baffles aregenerally circular and define a radial slit through which fluid mayflow. The slits of adjacent baffles are preferably at opposite sides ofthe coil 14 (i.e. at 180° relative to one another) forcing fluidtravelling up or down the conductive sheath to follow a generallyserpentine path. The conductive baffles 20 and 21 spaced between thehelical coils 12 and 14 also impart turbulence to the fluid heattransfer media in motion for enhancing heat transfer between coils 12and 14.

The outer coil 12 defines an exit point 22 at the top of the cylinderand an entry point 24 at the bottom of the cylinder, where fluids to beheated or cooled can enter and exit the coil 12. The entry and exitpoints can be reversed if desired.

Entry and exit points 26 and 28 respectively, for coolant or heatingmedia typically expanded refrigerant gas in the second helical coil 14,are located at the top and base of the heat exchanger 10.

The helical coils 12 and 14, the vessel 16 baffles and sheath may bemade of any suitable material. Typically stainless will be used for thehelical coils baffles and sheath particularly when used for beverageproducts such as beer and soft drinks. However the sheath and bafflesmay be made of any suitable conductive material.

FIG. 2 illustrates a pump 50 for pumping the fluid transfer mediumaround the coils 12, 14 in the housing. Fluid heat transfer media whenin motion, enters and exits at 30 and 32 respectively located at base ofheat exchanger 10.

The diameter of the tubes, the helical coils, the number of baffles, thelengths of the coil and the size of the housing and sheath can be variedto suit the particularly heat exchange requirements of the heat exchangesystem.

The inner or second helical coil 14 is sized to enable it to be insertedwithin the outer helical coil 12 with a gap between the inner surface ofthe helical coil and the outer surface of the helical coil 14 sufficientto enable the insertion of the conductive sheath 18. The gap can bevaried to suit the particular applications. In the illustrated examplethe gap is about 5 mm.

The housing 16 is filled with a heat transfer fluid which may be staticor in motion which remains in liquid form irrespective of thetemperature of the expanded refrigerant entering and exiting at 26 and28. The entire vessel containing the heat exchanger 10 may be enclosedin an insulated box.

The use of the heat exchanger 10 for dispensing beer in a smalldispensing and chilling installation in a restaurant or the like willnow be described, although it will be appreciated that the heatexchanger 10 may be used in many other applications.

The inlet 24 is connected to a keg or beer or the like and a small pumpor gas pressure is provided for transferring beer from the keg throughthe coil 12 to outlet 22 and the tap.

The second coil 14 is connected to a refrigeration unit. The refrigerantgas for cooling the heat exchanger typically passes through a TX valveor fixed orifice, to expand it prior to entry into the coil 14 via entry26 and exits the coil via the exit 28. For cooling beer, R404 or anequivalent refrigerant is the preferred refrigerant, although otherrefrigerants such as R134A, R22 could be used. The expansion of therefrigerant inside a coil rather than say in the vessel 16 itself,ensures that the refrigerant travels at a constant velocity and makesthe heat exchanger much easier to control. The refrigerant willtypically be at a temperature of around −4° C. The spacing of therefrigerant coil 14 from the coil containing beverage 12 reduces theefficiency of the heat transfer from the beverage to the refrigerant andlessens the likelihood of the beverage freezing within the heatexchanger, particularly when the heat exchanger is used infrequently, asis likely in a restaurant.

A number of heat exchange units as shown in FIG. 1, could be assembledtogether and share a common refrigerant line. A plurality of such unitswould allow for a multiple fluid steams of different fluids to heatedand cooled to differing temperatures and cooled simultaneously such asmay be required in an application such as a hotel, bar or club, Again,the diameter of the coils and the distance between the first and secondcoils could be varied as could their length, with the requirement beingthat the overall heat transfer coefficient between the refrigerant gasand the beverage, be increased or decreased based on specific heatexchange requirements.

Depending on the application, the diameter of the coils and the distancebetween the first and second coils, and the nature of the heat transfermedium whether static or in motion in terms of its heat transfercoefficient, and nature (fluid, or solid) could be varied to provideheat exchangers having particular characteristics to suit particularapplications.

Other uses envisaged for heat exchangers incorporating solid heattransfer media embodying the present invention include in cooling wateror other beverages where cross-contamination with either cooling fluidor heat transfer media has health implications and is to be avoided.

Similarly steam or hot water can be introduced into the same flow pathas the refrigerant gases for all heating applications where heatedfluids are to be generated.

Another suitable application for the heat exchanger embodying theinvention is for laboratory use where cooled liquids are required forcondensing vapours of exchanging to other fluid or gaseous media.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1. A heat exchanger including: an outer housing; a first means defininga first fluid flow path located in the housing, the first fluid 5 flowpath defining a plurality of turns and having an inlet and an outlet forentry and exit of fluid into the flow path to be heated or cooled; asecond means defining a second fluid flow path located within thehousing adjacent to the first flow path, said second fluid flow pathdefining a plurality of turns and having inlet and outlet for a passagefor hot or cold Service media; a sheath disposed between the first andsecond means; a transfer medium disposed in the housing for transfer ofheat between the first and second flow paths, using either a static or aflowing transfer medium; a plurality of baffles located between theouter housing and the sheath and disposed between turns of the firstfluid flow path; and a plurality of baffles disposed between turns ofthe second fluid flow path.
 2. A heat exchanger as claimed in claim 1wherein the sheath is made from a material having a relatively high heatconductivity such as a metal.
 3. A heat exchanger as claimed in claim 2wherein the baffles are made from a material having a relatively highheat conductivity such as a metal.
 4. A heat exchanger as claimed inclaim 1 wherein the sheath is made from a material having a relativelylow heat conductivity such as a plastics material.
 5. A heat exchangeras claimed in claim 1 wherein the baffles are made from a materialhaving a relatively low heat conductivity such as a plastics material.6. A heat exchanger as claimed in claim 1 wherein the first and secondfluid flow paths comprise helical coils with the second (inner) helicalcoil being of a relatively narrower diameter than the first (outer)helical coil and nested around the sheath which is located between thecoils.
 7. A heat exchanger as claimed in claim 6 wherein the helicalcoils have a circular cross section defining an interior and anexterior.
 8. Where conductive baffles are inserted into the helix ofeach fluid flow path coil between turns of the helix, these conferthermal energy to the coil as well as defining a generally serpentinefluid flow path for the transfer media when the transfer media is inmotion.
 9. A heat exchanger as claimed in claim 1 wherein the housing iscylindrical having an annular cross-section and most typically comprisesa metal or other material with a high coefficient of heat transfer. 10.A heat exchanger as claimed in claim 1 wherein the baffles locatedbetween the outer housing and the sheath comprise an annulus having adiscontinuity or slit extending between the interior and exterior of theannulus and are a close fit between the interior of the housing and theexterior of the sheath.
 11. A heat exchanger as claimed in claim 10wherein the slits in adjacent annuli are offset, typically by 180° toforce fluid travelling between the housing and the sheath to adopt aSerpentine flow-path.
 12. A heat exchanger as claimed in claim 1 whereinthe baffles located inside the sheath are circular plates having aradial slit extending from the circumference of the circular plate toabout its centre and are a close fit to the interior of the sheath. 13.A heat exchanger as claimed in claim 12 wherein the slits in adjacentcircular plates are offset, typically by 180° to force fluid travellingthrough the sheath to adopt a generally Serpentine flow-path.